Optimization of Packet Forwarding in Best-effort Routers

Miguel Ángel Ruiz Sánchez 1
1 PLANETE - Protocols and applications for the Internet
Inria Grenoble - Rhône-Alpes, CRISAM - Inria Sophia Antipolis - Méditerranée
Abstract : The main task of a router is to forward packets through the networks to deliver them to their final destination. Since each packet must be treated individually, the performance of a router depends on the time to process each packet. To keep pace with increasing traffic and wide spectrum of traffic requirements, the packet forwarding capacity of routers need to be optimized. This thesis proposes several algorithms to optimize the performance of the packet forwarding process in best effort routers.
To forward packets, routers must make a forwarding decision. The operation of determining the forwarding information is based on the packet's destination address and it is called address lookup. We propose in this thesis two incremental update mechanisms for address lookup schemes based on the multibit-trie data structure. First, we determine the requirements to support incremental updates in multibit-tries based forwarding databases.Then, we propose algorithms and data structures to support incremental updates. In particular, we propose a data structure called Prefix Nesting bit vector, or PN bit vector for short. The PN bit vector encodes a set of prefixes and their nesting structure, for this information is necessary to support incremental updates. We present performance results of a C-language implementation of our scheme. Performance results are shown in terms of time for the search, insert and delete operations. Memory requirements are also shown.
A second contribution of this thesis is the introduction of a taxonomy and a framework of reference of existing fast address lookup schemes. Our taxonomy is based on the observation that the difficulty of the best prefix matching problem resides in its double dimension: value and length. In our analysis, we emphasize that to improve the performance of the address lookup operation, the different methods make a transformation of the original set of prefixes of the forwarding database. We state the different tradeoffs of the different transformation methods in terms of time and space and we compare the performance of the different schemes. While the most important aspect is the search operation, we also analyze the potential capabilities of the schemes to support incremental updates. We state that to support incremental updates, a mechanism must have additional data structures to keep track of the prefix transformation process.
A third contribution of this thesis is a mechanism to optimize the use of the buffer in routers to provide fiow isolation. First, we study the buffering functionality of IP routers. We find the desired properties of a router buffer system, then we design a mechanism based on these characteristics. We emphasize that buffers in routers have two functions: a multiplexing function and a burst absorbing function. Our mechanism, which we call MuxQ, is based on the idea of protecting the multiplexing function from the burst absorbing function by progressively and dynamically controlling the allocation of buffer space in a FIFO queue. MuxQ is a new queue management mechanism that provides fiow isolation by using a very simple algorithm and without using per-fiow queuing. We compare the performance of the MuxQ scheme to that of classical Drop-Tail and to that of other proposed schemes, including CSFQ and DRR which provides nearly perfect isolation by using per-fiow queuing. By keeping only limited fiow-state, our mechanism performs very much better than Drop-Tail. MuxQ achieves performance similar to that of CSFQ but MuxQ does not need modifications to the IP packet header as it is the case for CSFQ. Since MuxQ does not need modifications of the IP packet header and does not expect a special behavior from other routers, MuxQ can be deployed incrementally. We believe that MuxQ is an interesting approach to achieve a high degree of fiow isolation with respect to Drop-Tail by using a very simple algorithm
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Submitted on : Friday, July 31, 2009 - 2:33:36 PM
Last modification on : Wednesday, April 11, 2018 - 1:52:04 AM
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Miguel Ángel Ruiz Sánchez. Optimization of Packet Forwarding in Best-effort Routers. Networking and Internet Architecture [cs.NI]. Université de Nice Sophia Antipolis, 2003. English. ⟨tel-00408685⟩

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